The present invention relates to electrical power supply circuits and, more particularly, to a power supply circuit which provides a substantially constant potential output signal but which limits the maximum output current to a predetermined current level.
There are many situations in which a high current power supply is required. Electrical power must be provided for powering various avionic systems when an airplane is on the ground with its engines off. Guidance, radio, radar, and other such systems require substantial power and it is highly desirable that this electrical power be carefully regulated. In aviation power systems operating on direct current, it is necessary to keep the ripple content of the power supply output at a minimum level to prevent interference with radio reception and with check out and operation of guidance systems.
Generally, electrical power for the engine starting motors is also provided by the same power supply. Since ground power supplies may be used with many different types of aircraft, it is desirable that such a power supply include a variable current limiting capability so that the maximum torque provided by the starting motors on various aircraft may be adjusted. If too great a starting current were permitted, the starting motors might provide a greater starting torque than can be tolerated and the aircraft might be damaged.
Engine generator sets cause substantial pollution and, therefore, are generally unacceptable as aviation ground power supplies inside a hanger or other enclosed structure. Motor generator sets powered by an electrical motor may be too noisy for some applications, such as check out of systems in an airplane assembly plant. Electrical-to-mechanical-to-electrical converters are also relatively inefficient at certain load levels. Various solid state AC-to-DC converters have in the past been used but these generally provide an undesirably high level of harmonic frequency superimposed on the DC output.
Thus it is seen that there is a need for a quiet, dependable static direct current power supply which provides an essentially ripple free output and which includes a means for limiting the maximum output current to a predetermined current level.